The present invention generally relates to apparatus and methods for accomplishing lubrication and cooling within a bearing compartment using separate fluid lubrication and cooling circuits. More specifically, the present invention relates to apparatus and methods relating to a multiple path fluid circuit comprising a lubrication fluid circuit and a cooling fluid circuit.
A fluid circuit for lubrication and cooling of certain components within an engine may include a fluid reservoir from which a lubrication fluid may be pumped by a fluid pump. The fluid pump may then deliver the fluid to a fluid circuit, which may include various conduits, annular passages, and the like which comprise a delivery means for the lubrication fluid, which may be used to deliver the pumped fluid to a moving component or to a component in contact with a moving component, which may require lubrication. Various moving components may be located within, or in fluid communication with, a bearing compartment having one or more fluid collection regions, or fluid sumps. Once the fluid exits the fluid delivery circuit and performs the required lubrication and cooling functions, (i.e., becomes spent fluid), it may then be collected in the fluid sump or sumps within the bearing compartment and returned to the reservoir through a scavenge circuit. The scavenge circuit may include various conduits, annular passages, fluid pumps, and the like which comprise a means for the spent fluid to be returned to the fluid reservoir. In some aspects, the energy to return the fluid to the reservoir is by means of a fluid pump, whereas in other aspects the energy is provided by the pressure within the bearing compartment, and may also include energy imparted to the fluid by the rotating components within the bearing compartment. The fluid may then be de-aerated, filtered, and cooled prior to re-use, either within the scavenge circuit, within the delivery portion of the circuit, or in any combination thereof.
Bearing compartments such as those in gas turbine engines may be located in engine sections that may be relatively hot compared to other sections of that same engine. Such bearing compartments may be referred to as hot section bearing compartments. Hot section bearing compartments may require provisions to moderate or cool the environment they may be in, in order to control the temperature of the air that leaks into the compartment, as well as the temperature of the internal oil-wetted walls of the compartment, and to facilitate the effectiveness of the oil introduced into the compartment to lubricate and cool various engine components within the bearing compartment. The temperature of the air that leaks into a hot section bearing compartment may be moderated by creating a buffer cavity that supplies the seals that seal the bearing compartment with air from a location of the engine, which may be cooler relative to the area where the hot section bearing compartment may be located. Examples of such cooler locations of a gas turbine engine may include a section where a compressor may be located. An additional means of controlling the thermal environment of a bearing compartment is to create a buffer cavity that completely surrounds the bearing compartment. To accomplish introduction of this cooling air into a buffer cavity surrounding a hot section bearing compartment, a region surrounding the buffer cavity may be vented to create a vent cavity wherein the pressure is reduced to a level below the pressure of the cooling air in the buffer cavity. Once the cooling air is introduced into the buffer cavity, it may leak into the hot section bearing compartment, and also leak into the vent cavity. Once in the vent cavity, the cooling air may be returned to the engine at some down stream location. As a result, multiple sets of air to air seals may be required to provide sealing between the buffer cavity and the vent cavity, and between the hot section environment and the vent cavity. In addition, cooling of a bearing compartment by introduction of cooling air around the compartment may result in an inefficiency to the engine due to the air lost by leakage into the bearing compartment, as well as through the addition of weight and complexity to the engine.
Regardless of whether or not the above described method for employing a buffer and vent cavity system is used, oil may be required within the bearing compartment to cool components within the compartment as well as to cool the internal oil-wetted walls of the compartment. In addition, oil may be required to lubricate surfaces of components within the bearing compartment that move relative to one another. To cool and to lubricate such internal components, a fluid (e.g., lubrication oil) may be supplied directly to a specific component via a lubrication fluid circuit with nozzles to control the quantity of fluid exiting the delivery passage and to direct the fluid to the appropriate location within the compartment. Once the fluid exits the lubrication fluid circuit (i.e., becomes unpressurized), it may come in contact with a surface or component and provide lubrication and cooling. Bearing compartment walls and other internal structures of the engine may also be cooled by splash action from the spent fluid. Once the fluid exits the fluid delivery circuit and performs the required lubrication and cooling functions, (i.e., becomes spent fluid), it may then be collected in the fluid sump or sumps within the bearing compartment and returned to the reservoir through a scavenge circuit.
In hot section bearing compartments, the amount of fluid needed for cooling may be greater than the amount of fluid that may be required for lubrication. Accordingly, if the spent fluid (e.g., oil) is not removed from the sump(s) within the compartment efficiently, churning of the fluid (i.e., energy added to the fluid by the rotating parts accompanied by increased aeration of the fluid) may result. Churning of spent fluid may result in heat generation, and may be detrimental to the sump and components located therein. Churning of spent fluid may also result in engine inefficiency, which may result in an engine being unable to meet a performance goal.
Also, lubrication systems may supply a fixed or predetermined amount of fluid flow to the various components and sumps regardless of an actual need dictated by engine operating conditions, or the condition of the lubrication system itself. Delivery of a fixed amount of fluid flow in excess of the flow required to achieve satisfactory lubrication and cooling may result in a lower efficiency of an engine.
Once an engine is shut down, the heat generated through operation of the engine may no longer be dissipated by systems which require the engine to be operating in order to function. Accordingly, various components may be subjected to temperatures brought about by so called “heat-soak”, or “soak-back”, wherein heat flows into previously cooler sections of an engine once the engine is shut down. Heat soak may result in degradation of various temperature sensitive components, including the lubrication fluid itself. As such, heat soak may also adversely affect engine performance and component longevity.
As can be seen, there is a need for improved apparatus and methods for providing engine fluid lubrication and cooling in which the detriment to engine performance may be minimized, the various components of an engine are protected, and the effects of heat soak on the engine may be reduced.